An ice storm is formed under a particular set of atmospheric conditions in which a layer of warm is sandwiched between two layers of cold air. Snow forms in the upper cold layer and passes through the warm air on its way towards the ground, melting into rain as it does so. This rain then passes through the lower layer of cold air but instead of freezing, it becomes supercooled. That is to say, the temperature of a drop of water will be below the freezing point (0°C) but will not have sufficient time to turn to ice. When this supercooled rain lands on a surface, it almost immediately freezes, coating the surface it landed on in a film of ice. These kinds of events are common in Canada. The reforestation program in Brampton was initiated in the wake of a major ice storm in 1998 and the city was again struck by another major ice storm only 15 years later in 2013. It is also likely that freezing rain and ice storms are going to be more common in the Winter months in Southern Ontario and Quebec, with some reports indicating the potential for a 40% increase in such incidents.
After a major ice storm in 1998, the City of Brampton embarked on an ambitious program of tree planting to help recuperate losses to the tree canopy while simultaneously increasing resilience to such events in the future. The 1998 Ice Storm caused significant damage across Southern Ontario and Quebec. It was officially recorded as the first storm in Canada to cause over a billion dollars in losses and was responsible for 35 deaths, 935 injured persons, and the temporary displacement of roughly 600,000 across the affected area. This storm also caused widespread devastation to the local tree canopy as the ice accumulating on the branches of trees eventually caused branches to break off or the tree to topple entirely. Rehabilitating the tree canopy has been on ongoing process that has suffered some setbacks, such as another major ice storm in 2013 that again caused extensive damage to the canopy, revealing problems with the tree selection process but also providing the opportunity to learn and refine the approach.